This invention relates to a tree felling unit of the kind, which comprises a stand, a saw chain within the stand, and at least one clamping device for clamping the tree to be felled against the stand.
For machine felling of trees two types of felling units exist, which are different in principle, to wit, units shearing off the trees and units sawing off the trees. The firstmentioned type of felling unit is equipped with hydraulically or pneumatically operated shearing devices provided with knives, by means of which the trees are sheared off. These shearing felling units have the advantage of working relatively rapidly and, therefore, they can advantageously be utilized particularly in the case of a tree of small-dimension. It was, however, found that on trees of greater dimensions these felling units cause considerable wood and splinter damages because of the large pressure forces, which are required for shearing off the tree and applied substantially perpendicularly to the fibre direction in the tree. These wood and splinter damages cause large timber losses particularly on saw timber.
Since recently, therefore, felling units to a certain extent are equipped with a saw chain, which by its cutting mode of operation treats the tree much more gently than do shearing devices and does not give rise to any wood or splinter damages. This type of felling unit, on the other hand, operates much slower than the shearing felling units and, besides, the felling units equipped with a saw chain have the disadvantage, that immediately before and especially at the moment of through-sawing they are not capable of holding the tree so firmly that pinching and clamping of the saw chain is prevented. The trees, by their own weight, and their swinging moment inherent or imparted to them during the sawing operation, usually subject the saw chain to extraordinary stresses with resulting damages of the chain and/or its drive mechanism.
The present invention, therefore, has the object of eliminating to the greatest possible extent the disadvantages of the known felling units with saw chain and, more precisely, of producing a felling unit with saw chain which is much more reliable in operation and works faster than the known units of this kind. This object is achieved thereby that the felling unit according to the present invention shows the characterizing features defined in the claims.